The present invention relates to a unit-to-unit register adjusting apparatus and method for adjustably bringing into mutual superimposition images printed by printing units for different colors in a multicolor sheet-fed rotary printing press.
Multicolor printing presses effect multicolor printing on a web at one position thereof or on a single sheet. Production of prints of good quality requires that the images printed by the successive printing units for different colors be brought into complete superimposition. To effect such an operation, each printing unit has a register adjusting apparatus for displacing a plate or a plate cylinder on which the plate is mounted in various directions. Register adjustment in the circumferential direction and the axial direction of the plate cylinder can be effected while the multicolor printing press is in operation by displacing the plate cylinder in the desired directions under remote control. With web-fed printing presses, skewing adjustment for correcting a plate out of circumferential displacement on a plate cylinder into proper lateral phase relation to the latter can also be carried out during operation of the printing press since register errors are relatively small and the plate cylinder can be skewed within a range in which the ball or roller bearings can be skewed.
However, sheet-fed rotary printing presses tend to suffer from relatively large register errors, and it is difficult to perform skewing adjustment while the press is being operated. A customary practice has been to stop the operation of the press, and then skew the plate into correct position relative to the plate cylinder. More specifically, the plate to be skewed into proper position is gripped at opposite ends by plate clamping devices disposed in a groove in a circumferential surface of the plate cylinder. The skewing of the plate for register adjustment is done by displacing the plate clamping devices with the plate gripped thereby with respect to the plate cylinder since there would be the danger of causing a skewing error if the plate clamping devices were loosened and tightened again to grip the plate. The skewing process is as follows: The plate clamping device on the leading side is properly affixed to the plate cylinder and grips the front end of the plate. The plate is wound around the plate cylinder and the rear end of the plate is gripped by the plate clamping device on the trailing side. The plate is completely mounted on the plate cylinder by pulling the trailing plate clamping device circumferentially of the plate cylinder. If the plate has been found to be improperly skewed with respect to the plate cylinder upon examination of the printed colors of a print, then the plate clamping device on the trailing side is loosened from the plate cylinder, the plate clamping devices on the leading and trailing sides are skewed back for required intervals, and the trailing plate clamping device is pulled in the circumferential direction of the plate cylinder, thus completing the skewing adjustment.
The foregoing procedure of skewing adjustment, however, is disadvantageous in that the positions in which the plate clamping devices are fixed and adjusted with respect to the plate cylinder differ dependent on the pitches of correction screws, and the actual amount of adjustment is liable to not be in agreement with the required amount of adjustment, which has been determined upon test printing. The prior skewing adjustment requires much skill on the part of the operator, is time-consuming as it needs repeated correction steps, and results in a large amount of spoilage or wasted printed material which is produced while the skewing adjustment is being made.